1. Field of the Invention (Technical Field)
The present invention relates to modularization of photovoltaic systems. The invention provides a fully integrated and self-contained alternating current (xe2x80x9cACxe2x80x9d) photovoltaic (xe2x80x9cPVxe2x80x9d) Building Block device and method that allows photovoltaic applications to become true plug-and-play devices.
2. Background Art
Note that the following discussion refers to a number of publications by author(s) and year of publication, and that due to recent publication dates certain publications are not to be considered as prior art vis-a-vis the present invention Discussion of such publications herein is given for more complete background and is not to be construed as an admission that such publications are prior art for patentability determination purposes.
Today""s photovoltaic power systems are generally comprised of a single photovoltaic module or multiple modules that are connected by combinations of series and parallel circuits as a photovoltaic array. In the case of a single module system producing AC power output, the photovoltaic module is connected to the inverter or load through a junction box that incorporates a fuse to protect the photovoltaic module if backfeeding from other sources (e g; a power utility or a battery) is possible. The photovoltaic modules used in these systems are configured either with a frame or without a frame Frameless photovoltaic modules are generally referred to as a laminate. For conventional systems that utilize multiple laminates or modules, the laminates or modules are interconnected via junction boxes or flying leads and external wiring that must be rated sunlight resistant and sized to carry the rated currents. Some conventional photovoltaic system installations require that the direct current (xe2x80x9cDCxe2x80x9d) and AC wiring be installed in properly sized and anchored conduit.
A typical method of interconnecting the DC circuits in a conventional photovoltaic system is to have a J-box at the top of each photovoltaic module that provides the terminal block to connect the module circuit to flying-lead conductors that are then fitted with a connector. The J-box also houses the series or xe2x80x9cblockingxe2x80x9d diode often required by codes and standards to protect the module, especially if more than two strings of modules are paralleled at the combiner box or at the inverter The module is often constructed with a bypass diode(s) that is(are) usually required for conventional photovoltaic applications. This arrangement is used to connect modules in series. Modules are connected in series until the summed operating voltage is within the optimum DC voltage window of the central or string inverter. The connections are typically made under the modules by plugging connectors together or at distributed junction boxes. Some installations leave insufficient space to allow the installer to make the connections reliably. The central inverter can generally handle multiple strings of photovoltaic modules that are then wired in parallel in a stnng-combiner assembly or box before DC power is fed to the inverter.
FIG. 1 illustrates a typical conventional grid-connected photovoltaic system. An array 10 of modules or laminates 11 (each includes bypass diodes) of solar cells 12 is employed, the modules or laminates being in series and parallel combinations. The array is typically required to be grounded. Module interconnect wiring 13 (sometimes requiring conduit) provides power through fuses 14 (typically in module J-boxes) to photovoltaic source circuits 15 (requires wiring and sometimes conduit) to blocking or series diodes 16 typically in combiner box 17 (which may also house surge protection). Photovoltaic output circuit 18 (wiring with conduit) then passes power on to DC disconnect box 19 with PV output overcurrent protection. Wiring 9 (sometimes with conduit) then passes power on to inverter 8 with associated housing (often including ground fault protection), which then passes AC power to AC disconnects, fuses, and surge protection 6 and then on to an AC dedicated branch circuit 5 originating at the service panel
The AC PV Building Block of the present invention eliminates all DC wiring, the requirement for the fuse, the need for bypass diodes or series diodes, the J-box, and connections. All connections except the final AC connections are part of the integrated package of the invention.
FIG. 2 illustrates a typical grid-connected photovoltaic system according to the invention AC PV. Building Block array 22 comprises modules or laminates 24, each comprising solar cells 26 Power bars or rails 20 attached to the modules each comprise an inverter and AC bus, as well as typically communications and protection hardware A plurality of interconnect bars or rails 28 are attached to a portion of the array and linked to connect a plurality of AC PV Building Blocks in parallel while transferring power and communications via a central point of connection. Power is provided over wiring 25 (sometimes with conduit) to AC disconnects, fuses, and surge protection 23, and then on to AC dedicated branch circuit 21 originating at the service panel. The AC PV Building Block of the invention eliminates all of the external DC hardware and issues associated with conventional systems and houses the collective AC bus, leaving requirements only for the AC-side disconnects, wiring and interconnects that are very familiar to electricians and electrical contractors. Furthermore, voltages seen by the PV panels/cells never gets to be high because the modules are connected in parallel rather than series. This improves reliability of the PV panel contacts and overall reliability.
The AC PV Building Block of the invention can be employed with any size and/or shape of photovoltaic system that provides AC power to: (1) the utility grid; (2) mini-grids utilizing other sources of AC electrical generation often referred to hybrid systems; or (3) stand-alone power systems that typically use electrical energy storage and an inverter to supply AC power to off-grid loads such as remote residences, communications stations, emergency lighting and the multitude of remote energy systems requiring AC power.
Additionally, the invention can be combined to form complete photovoltaic energy systems that use a single or multiple photovoltaic modules where the entire power interconnection, conversion, protection and combining can take place within a listed or certified structure that also is used to mount, attach and join photovoltaic modules.
The following U.S patents relate generally to the state of the art in photovoltaic systems U.S. Pat. No. 6,219,623, to Wills; U.S. Pat. No. 6,285,572, to Onizuka; U S. Pat. No. 6,201,180, to Meyer; U.S. Pat. No. 6,143,582, to Vu; U.S. Pat. No. 6,111,189, to Garvison; U.S. Pat. No. 6,046,400, to Drummer; U.S. Pat. No. 5,742,495, to Barone; and U.S. Pat. No. 5,702,963, to Vu.
Pacific Solar manufactures Plug and Power and SunEmpower Systems that employ a micro-inverter. However, the micro-inverter is a separate component that is not physically attached to the photovoltaic panel. Rather, the micro-inverter is electrically interconnected via separate cables to the photovoltaic panel. Furthermore, all interconnects are via cables for the DC-side and also the AC side. The National Electrical Code(copyright) in the United States and related codes and standards internationally still require DC fuses, ground-fault detection/interruption, DC disconnects and grounding of the DC side with the Plug and Power/SunEmpower design of Pacific Solar. Further, the installation costs for the Plug and Power/SunEmpower design are increased by the required interconnect devices, the need for a separate inverter housing, and the housing required for J-boxes and/or combiners.
The SunSine(copyright) 300 product of Applied Power Corporation also employs a micro-inverter However, exposed cabling is employed to connect each panel""s micro-inverter to adjacent panels"" micro-inverters.
The following references additionally relate to the state of the art in photovoltaic systems Stevens, J., et al., xe2x80x9cDevelopment and Testing of an Approach to Anti-islanding in Utility-Interconnected Photovoltaic Systemsxe2x80x9d, SAND2000-1939, Sandia National Laboratories, Albuquerque, N.Mex. (August 2000); IEEE Recommended Practice for Utility Interface of Photovoltaic (PV) Systems, IEEE Standards Coordinating Committee 21 on Photovoltaics, IEEE Std. 929-2000, IEEE, New York, N.Y., (April 2000); UL Standard for Safety for Static Converters and Charge Controllers for Use in Photovoltaic Power Systems, UL1741, Underwriters Laboratories, First Edition (May 1999): Ropp, M., et al., xe2x80x9cPrevention of Islanding in Grid-connected Photovoltaic Systems,xe2x80x9d Progress in Photovoltaics Research and Applications, John Wiley and Sons, Volume 7, Number 1 (January-February 1999); Bower, W., et al., xe2x80x9cInvestigation of Ground-Fault Protection Devices for Photovoltaic Power Systems Applications,xe2x80x9d Proceedings of the 28th IEEE Photovoltaic Specialist Conference, Anchorage, Ak. (Sep. 15-22, 2000). Kern, G, SunSine(trademark)300. Manufacture of an AC Photovoltaic Module, A PVMaT Contractors Final Report by Ascension Technology, Phases I and II, NREUSR-520-26085, Golden, Colo. (March 1999); Begovic, M., et al., xe2x80x9cDetermining the Sufficiency of Standard Protective Relaying for Islanding Prevention in Grid-Connected PV Systems,xe2x80x9d Proceedings of the 2nd World Conference and Exhibition on Photovoltaic Solar Energy Conversion, Hofburg Congress Center, Vienna, Austria (Jul. 6-10, 1998); Kleinkauf, W., et al., xe2x80x9cStandardization of Systems Technology for PV Power Supplyxe2x80x94Modular Structures With Series Produced Components,xe2x80x9d Proceedings of the 2nd World Conference and Exhibition on Photovoltaic Solar Energy Conversion, Hofburg Congress Center, Vienna, Austria (Jul. 6-10, 1998); Stem, M., et al., Development of a Low-cost, Integrated 20-kW AC Solar Tracking Sub-Array for Grid-connected PV Power System Applications, A PVMaT Final Technical Report by Utility Power Group, NREUSR-520-24759 (June 1998); Kern, G.A., xe2x80x9cInterconnect Guidelines and Status of AC PV Modules in the United States,xe2x80x9d Proceedings of the IEA PVPS Task V Workshop on Utility Interconnection of PV Systems, Zurich, Switzerland (Sep. 15-16, 1997); Russell, M., et al., Sunsine 300 AC Module, A PVMaT Annual Report by Ascension Technology, NREL/SR-520-23432, Golden, Colo. (August 1997); Strong, S., et al., Development of Standardized Low-Cost AC PV Systems: Phase I Annual Report, A PVMaT Contractors Report by Solar Design Associates, Solarex and Advanced Energy Systems, NREUSR-520-23002, Golden, Colo. (June 1997); Odenkamp, H., et al., xe2x80x9cReliability and Accelerated Life Tests of the AC Module-mounted OKE4 Inverter,xe2x80x9d Proceedings of the 25th IEEE Photovoltaic Specialists Conference, Washington, DC (May 13-17, 1996); Bower, W., xe2x80x9cSandia""s PV Program Perspectives on xe2x80x9cSmart Powerxe2x80x9d and Power Integrated Circuit Devices for Photovoltaic Applications,xe2x80x9d Proceedings of 2nd Workshop on Smart Power/Power Integrated Circuit Technology and Applications, Pasadena, Calif. (Dec. 8-9, 1994); Bower, W., et al., xe2x80x9cAnalysis of Grounded and Ungrounded Photovoltaic Systems,xe2x80x9d Proceedings of the 1st World Conference on Photovoltaic Energy Conversion, Waikoloa, Hi. (Dec. 5-9, 1994), Bower, W., et al., xe2x80x9cCertification of Photovoltaic Inverters,xe2x80x9d Proceedings of the Photovoltaics Systems Symposium, Albuquerque, N.Mex. (Jul. 18-20, 2001); Martin, B., xe2x80x9cDeveloping a PV Practitioner Certification Programxe2x80x9d, 2001 Workshop Paper, Sacramento, Calif. (Sep. 30, 2001); Bower, W., et al., xe2x80x9cCertification Of Photovoltaic Inverters: The Initial Step Toward PV System Certification,xe2x80x9d Proceedings of the IEEE 29th PV Specialist Conference, New Orleans, La. (May 21-24, 2002); Objectives and Task Analysis for the Solar Photovoltaic System Installer, North American Board of Certified Energy Practitioners"" Technical Committee Document, available at www.nabcep org.
The present invention is of a modular apparatus for and method of alternating current photovoltaic power generation, comprising: via a photovoltaic module, generating power in the form of direct current; and converting direct current to alternating current and exporting power via one or more power conversion and transfer units attached to the module, each unit comprising a unitary housing extending a length or width of the module, which housing comprises: contact means for receiving direct current from the module; one or more direct current-to-alternating current inverters; and an alternating current bus. An alternating current bus link attached to the bus permits parallel interconnection to other apparatuses according to the invention to form an AC photovoltaic array. Data may be communicated via a data communications link comprised by the housing. One or more interconnect units may be attached to the module and electrically connected to the alternating current bus to an external connection point for the alternating current power to an electrical service panel. The housing provides physical modularity by employing an Ibeam shape, a channel shape, or a T-beam shape. The housing may additionally comprise any or all of the following a surge protector for the one or more inverters and photovoltaic module, a communications network that reports status information, a communications network for dispatching or other selection criteria, seals to provide weather resistance, and thermal management means. The module may be framed, roof mounted, open structure mounted, pole mounted, or window wall mounted. No external direct current fuses or direct current disconnects are needed.
The invention is also of an alternating current photovoltaic power generation system comprising one or a plurality of the modular alternating current photovoltaic power generation apparatuses just described.
The invention is additionally of a modular apparatus and method for generating alternating current photovoltaic power, comprising: via a photovoltaic module, generating power in the form of direct current; receiving the direct current and converting to alternating current via one or more direct current-to-alternating current inverters; and exporting the alternating current via one or more power transfer units attached to the module, each unit comprising a unitary housing extending a length or width of the module, which housing comprises: contact means for delivering direct current to the one or more inverters and contact means for receiving alternating current from the one or more inverters; and an alternating current bus.
The invention is further of a modular photovoltaic power generation apparatus comprising a photovoltaic panel comprising an edge; a hollow structural member attached to the edge of the panel; and a direct current-to-alternating current inverter module attached to the structural member. The apparatus may further comprise an alternating current bus disposed inside of the hollow structural member and interconnect means, disposed inside of the hollow structural member, for transferring direct current from the photovoltaic panel to the inverter module.
Objects, advantages and novel features, and further scope of applicability of the present invention will be set forth in part in the detailed description to follow, taken in conjunction with the accompanying drawings, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.